Mutant eyes lack the prolonged depolarizing afterpotential (PDA) that is induced in wild-type R1-6 photoreceptors by a bright or prolonged blue light stimulus, which photoconverts a large fraction of rhodopsin in these photoreceptors to metarhodopsin; inaA1-induced phenotype differs from that observed in nina mutants because the R1-6 photoreceptors of ina mutants are inactivated after the blue stimulus, i.e., are insensitive to subsequent blue light stimuli; an orange light stimulus, which cancels the PDA of wild type by photoconverting metarhodopsin back to rhodopsin, restores the R1-6 cell sensitivity of ina mutants.
